Comparison circuit including input sampling capacitor and image sensor including the same

ABSTRACT

A comparison circuit that includes an input sampling capacitor and an image sensor including the same are provided. The comparison circuit includes an amplifier configured to receive a pixel signal and a ramp signal to perform a correlated double sampling operation, a first pixel capacitor connected to the amplifier through a first floating node and configured to transmit the pixel signal, a first ramp capacitor connected to the amplifier through a second floating node and configured to transmit the ramp signal, a second pixel capacitor connected in parallel to the first pixel capacitor, and a second ramp capacitor connected in parallel to the first ramp capacitor, wherein the second pixel capacitor is formed between the first floating node and first peripheral routing lines, and the second ramp capacitor is formed between the second floating node and second peripheral routing lines.

CROSS-REFERENCE TO THE RELATED APPLICATION

This application claims priority from Korean Patent Application No.10-2016-0096339, filed on Jul. 28, 2016, in the Korean IntellectualProperty Office, the entire contents of which are hereby incorporated byreference.

BACKGROUND

Apparatuses consistent with example embodiments relate to image sensors,and more particularly, to a comparison circuit including an inputsampling capacitor and an image sensor including the same.

An image sensor converts an optical image into an electrical signal. Asa computer industry and a communication industry develop, the demand foran image sensor having improved performance in various fields such as adigital camera, a camcorder, a personal communication system (PCS), agame machine, a security camera, a medical micro camera, etc. is beingincreased.

The image sensor includes a charge coupled device (CCD) and acomplementary metal-oxide-semiconductor (CMOS) image sensor. Because theCMOS image sensor has a simple driving method and can integrate a signalprocessing circuit in a single chip, the CMOS image sensor is ofadvantage to miniaturization of the product. The CMOS image sensor hasvery low power consumption and thus can be easily applied to the producthaving a limited battery capacity. Because the CMOS image sensor can bemanufactured using a compatible CMOS process technology, a manufacturingcost of the CMOS image sensor may be lowered. Thus, the use of the CMOSimage sensor is rapidly being increased according to a technologydevelopment and an implementation capability of the CMOS image sensor.

The CMOS image sensor includes a comparison circuit. The comparisoncircuit compares a signal sensed in a sensor array of the CMOS imagesensor and a ramp signal generated in a ramp generator to generate adigital signal. The signal sensed in the sensor array and the rampsignal are affected by a plurality of capacitors while they aretransmitted to an amplifier of the comparison circuit. The capacitorsinclude predetermined capacitors and parasitic capacitors. Transmissionefficiency in the comparison circuit is determined according to a ratioof the predetermined capacitors to the parasitic capacitors.

SUMMARY

According to an aspect of an example embodiment, there is provide acomparison circuit including an amplifier configured to receive a pixelsignal and a ramp signal to perform a correlated double samplingoperation, a first pixel capacitor connected to the amplifier through afirst floating node and configured to transmit the pixel signal, a firstramp capacitor connected to the amplifier through a second floating nodeand configured to transmit the ramp signal, a second pixel capacitorconnected in parallel to the first pixel capacitor, and a second rampcapacitor connected in parallel to the first ramp capacitor. The secondpixel capacitor may be formed between the first floating node and firstperipheral routing lines, and the second ramp capacitor may be formedbetween the second floating node and second peripheral routing lines.

According to an aspect of another example embodiment, there is providean image sensor including a sensor array configured to convert a lightinto an electrical signal to generate a pixel signal, a ramp signalgenerator configured to generate a ramp signal, and a comparison circuitconfigured to receive the pixel signal and the ramp signal to perform acorrelated double sampling operation. The comparison circuit may includean amplifier configured to perform the correlated double samplingoperation, a first pixel capacitor configured to be connected to theamplifier through a first floating node and to transmit the pixelsignal, a first ramp capacitor configured to be connected to theamplifier through a second floating node and to transmit the rampsignal, a second pixel capacitor configured to be connected in parallelto the first pixel capacitor, and a second ramp capacitor configured tobe connected in parallel to the first ramp capacitor. The second pixelcapacitor is formed between the first floating node and first peripheralrouting lines, and the second ramp capacitor is formed between thesecond floating node and second peripheral routing lines.

According to an aspect of another example embodiment, there is provide acomparison circuit including an amplifier configured to receive a pixelsignal and a ramp signal to perform a correlated double samplingoperation, an input capacitor comprising a pixel capacitor and a rampcapacitor and having a predetermined capacitance, and a plurality ofparasitic capacitors, wherein a parasitic capacitor, among the parasiticcapacitors, formed at a floating node between the input capacitor andthe amplifier is converted into an input capacitor by changing a layoutof the comparison circuit to increase capacitance of the inputcapacitor, the changing the layout of the comparison circuit comprisingconnecting the parasitic capacitor formed at the floating node inparallel to the input capacitor.

BRIEF DESCRIPTION OF THE FIGURES

Example embodiments will be described below in more detail withreference to the accompanying drawings, in which:

FIG. 1 is a block diagram illustrating an image sensor according to anexample embodiment;

FIG. 2 is a view illustrating a comparison unit illustrated in FIG. 1 indetail;

FIG. 3 is a view conceptually illustrating a layout of one ofcomparators illustrated in FIG. 2;

FIG. 4 is a circuit diagram illustrating a connection relation ofcapacitors in one of comparators illustrated in FIG. 2;

FIG. 5 is a conceptual diagram corresponding to a cross section takenalong the line A-A′ in FIG. 3 to implement a connection relation ofcapacitors illustrated in FIG. 4;

FIG. 6 is a circuit diagram illustrating a connection relation ofcapacitors according to an example embodiment in one of comparatorsillustrated in FIG. 2;

FIG. 7 is a conceptual diagram corresponding to a cross section takenalong the line A-A′ in FIG. 3 to implement a connection relation ofcapacitors illustrated in FIG. 6;

FIG. 8 is a view illustrating a camera system including an image sensoraccording to an example embodiment;

FIG. 9 is a block diagram illustrating a configuration of an electronicdevice including an image sensor according to an example embodiment andinterfaces of the electronic device.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

Below, example embodiments of the inventive concept will be described indetail with reference to the accompanying drawings. This inventiveconcept may, however, be embodied in many different forms and should notbe construed as limited to the example embodiments set forth herein.Rather, the example embodiments are provided so that this disclosurewill be thorough and complete, and will fully convey the scope of theinventive concept to those skilled in the art. In the drawings, the sizeand relative sizes of layers and regions may be exaggerated for clarity.Like numbers refer to like elements throughout.

FIG. 1 is a block diagram illustrating an image sensor 100 according toan example embodiment. Referring to FIG. 1, the image sensor 100 mayinclude a timing signal generator 110, a row driver 120, a sensor array130, a ramp signal generator 140, a comparison unit 150, and a countingunit 160.

The timing signal generator 110 generates a timing signal in response toa control signal for generation of timing signals. The timing signalgenerator 110 may generate a row driver control signal (RD_con) thatcontrols an operation of the row driver 120. The timing signal generator110 may generate a ramp enable signal (RMP_en) that controls anoperation of the ramp signal generator 140. The timing signal generator110 may generate a counter enable signal (CNT_en) that controls anoperation of the counting unit 160.

The row driver 120 sequentially drives a plurality of rows of the sensorarray 130 in response to the row driver control signal (RD_con). The rowdriver 120 may be electrically connected to the plurality of rows of thesensor array 130. Pixels of a selected row may convert a sensed lightinto a pixel signal VPIX which is an electrical signal.

The sensor array 130 includes a plurality of optical sensing devices.The sensor array 130 includes a plurality of rows and a plurality ofcolumns. The plurality of optical sensing devices may be disposed atpositions in which the rows cross the columns.

An optical sensing device may be a photo diode, a photo transistor, aphoto gate, a pinned photo diode (PPD), or combinations thereof. Forexample, the optical sensing device may have a 4-transistor structureincluding a photo diode, a transmission transistor, a reset transistor,an amplifying transistor, and a select transistor. The optical sensingdevice may have a 1-transistor structure, a 3-transistor structure, a5-transistor structure, or a structure in which a plurality of pixelsshare some transistors. The sensor array 130 may convert a sensed lightinto a pixel signal VPIX to transmit the converted pixel signal VPIX tothe comparison unit 150.

The ramp signal generator 140 generates a ramp signal VRMP in responseto the ramp enable signal (RMP_en). A voltage level of the ramp signalVRMP may increase or decrease in proportion to the elapsed time. Theramp signal VRMP may be transmitted to the comparison unit 150 to beused to convert an analog signal into a digital signal.

The comparison unit 150 receives the ramp signal VRMP and the pixelsignal VPIX. The comparison unit 150 compares the ramp signal VRMP andthe pixel signal VPIX to transmit a comparison signal COMOUT to thecounting unit 160. The comparison unit 150 may perform an operation of acorrelated double sampling (CDS) to reduce a noise. Thus, the comparisonunit 150 may further include a CDS circuit that extracts a signal havingno noise from a difference between the ramp signal VRMP and the pixelsignal VPIX.

The counting unit 160 may generate a counting signal corresponding tothe ramp signal VRMP in response to the counter enable signal (CNT_en).When the ramp signal VRMP begins, the counting unit 160 may begin acounting operation. The counting unit 160 may convert the comparisonsignal COMOUT received from the comparison unit 150 into digitalinformation to output pixel data PDATA.

The comparison unit 150 may include a plurality of comparators. Eachcomparator may receive the ramp signal VRMP and the pixel signal VPIX.Each comparator may include an amplifier that compares the ramp signalVRMP and the pixel signal VPIX. Each of the ramp signal VRMP and thepixel signal VPIX is transmitted to the amplifier through an inputcapacitor. Each comparator may include various parasitic capacitors inaddition to the input capacitor. The parasitic capacitor may be formedat a floating node between the input capacitor of each comparator andthe amplifier. Each comparator may convert the parasitic capacitorformed at the floating node into the input capacitor by changing alayout of the comparator. Thus, in each comparator, capacitance of theparasitic capacitor is reduced and capacitance of the input capacitorincreases.

A transmission efficiency of each comparator depends on capacitance ofthe capacitors. For example, if capacitance of the input capacitorincreases, a transmission efficiency of each comparator may increase. Ifcapacitance of the parasitic capacitor increases, a transmissionefficiency of each comparator may be reduced. Thus, in each comparator,if capacitance of the parasitic capacitor is reduced and capacitance ofthe input capacitor increases, a transmission efficiency of eachcomparator may increase.

FIG. 2 is a view illustrating a comparison unit 150 illustrated in FIG.1 in detail. Referring to FIG. 2, the sensor array 130 may include aplurality of columns. The comparison unit 150 may include a plurality ofcomparators (151 to 15 n) connected to the plurality of columns of thesensor array 130. The ramp signal generator 140 may generate the rampsignal VRMP in response to the ramp enable signal (RMP_en). Thegenerated ramp signals VRMP may be equally supplied to the respectivecomparators (151 to 15 n).

Each of pixels of the sensor array 130 may convert a light into anelectrical signal. Pixels connected to a selected row of the sensorarray 130 may output pixel signals (VPIX1 to VPIXn). Each of thecomparators (151 to 15 n) compares the ramp signal VRMP with each of thepixel signals (VPIX1 to VPIXn) to output comparator signals (COMOUT1 toCOMOUTn). The first comparator 151 may compare the ramp signal VRMP withthe first pixel signal VPIX1 to output the first comparator signalCOMOUT1. The second comparator 152 may compare the ramp signal VRMP withthe second pixel signal VPIX2 to output the second comparator signalCOMOUT2. The nth comparator 15 n may compare the ramp signal VRMP withthe nth pixel signal VPIXn to output the nth comparator signal COMOUTn.

Each of the comparators (151 to 15 n) may perform a correlated doublesampling (CDS) operation. Each of the comparators (151 to 15 n) mayperform the CDS operation using the ramp signal VRMP and each of thepixel signals (VPIX1 to VPIXn). The generated comparator signals(COMOUT1 to COMOUTn) are transmitted to counters (not illustrated)included in the counting unit 160. The counters included in the countingunit 160 may count the respective comparator signals (COMOUT1 toCOMOUTn) to convert the counted value into a digital code.

According to an example embodiment, the comparators (151 to 15 n) mayreceive the ramp signal VRMP and respective pixel signals (VPX1 toVPXn). In each of the comparators (151 to 15 n), the pixel signal VPXand the ramp signal VRMP are transmitted to an amplifier through aninput capacitor. Each of the comparators (151 to 15 n) may includevarious parasitic capacitors in addition to the input capacitor. Theparasitic capacitor may be formed at a floating node between the inputcapacitor of each of the comparators (151 to 15 n) and the amplifier.Each of the comparators (151 to 15 n) may convert the parasiticcapacitor formed at the floating node into the input capacitor through achange of the layout. Thus, capacitance of the parasitic capacitor maybe reduced and capacitance of the input capacitor may increase in eachof the comparators (151 to 15 n).

Transmission efficiency of each of the comparators (151 to 15 n) isdetermined by capacitance of capacitors. If capacitance of the inputcapacitor increases, transmission efficiency of each of the comparators(151 to 15 n) may increase. If capacitance of the parasitic capacitorincreases, transmission efficiency of each of the comparators (151 to 15n) may be reduced. Thus, if capacitance of the parasitic capacitor isreduced and capacitance of the input capacitor increases in each of thecomparators (151 to 15 n), transmission efficiency of each of thecomparators (151 to 15 n) may be improved.

FIG. 3 is a view conceptually illustrating a layout of one ofcomparators illustrated in FIG. 2. Referring to FIG. 3, the comparator151 may include a pixel capacitor Cpix, a ramp capacitor Crmp and anamplifier OTA. The pixel capacitor Cpix and the ramp capacitor Crmp areinput capacitors configured to have predetermined capacitance.

The pixel capacitor Cpix may be configured to have a predeterminedcapacitance. For example, the pixel capacitor Cpix may be configured tohave a fixed first width W1 in a first direction D1 and to have apredetermined length in a second direction D2 perpendicular to the firstdirection D1 according to the predetermined charge capacitance. Thepixel capacitor Cpix may be stacked in a third direction D3perpendicular to the first and second directions D1 and D2. However, themethod of forming the pixel capacitor Cpix according to exampleembodiments is not limited thereto. The pixel capacitor Cpix may beconnected to the amplifier OTA through a floating node INN and afloating node contact INNC.

The ramp capacitor Crmp may be configured to have a predetermined chargecapacitance. For example, the ramp capacitor Crmp may be configured tohave the fixed first width W1 in the first direction D1 and to have apredetermined length in the second direction D2 perpendicular to thefirst direction D1 according to a predetermined charge capacitance. Theramp capacitor Crmp may be stacked in the third direction D3perpendicular to the first and second directions D1 and D2. However, themethod of forming the ramp capacitor Crmp according to exampleembodiments is not limited thereto. The ramp capacitor Crmp may beconnected to the amplifier OTA through a floating node INP and afloating node contact INPC.

The pixel capacitor Cpix and the ramp capacitor Crmp may be disposed inparallel along the second direction D2. A length of the floating nodeINN may be formed the same as a length of the floating node INP toreduce an effect of a parasitic capacitance. A parasitic capacitor maybe formed between the floating node INN, peripheral routing lines andthe floating node INP. The amplifier OTA may include a plurality oftransistors.

FIG. 4 is a circuit diagram illustrating a connection relation ofcapacitors in one of comparators illustrated in FIG. 2. Referring toFIG. 4, a comparator 151 a may include a pixel capacitor Cpix, a rampcapacitor Crmp and an amplifier OTA. The pixel capacitor Cpix and theramp capacitor Crmp are predetermined input capacitors for improving anoise characteristic. The first pixel signal VPIX1 is transmitted to theamplifier OTA through the pixel capacitor Cpix. The ramp signal VRMP istransmitted to the amplifier OTA through the ramp capacitor Crmp. Thepixel capacitor Cpix, the ramp capacitor Crmp, the amplifier OTA, afloating node INN, and a floating node INP of FIG. 4 correspond to thepixel capacitor Cpix, the ramp capacitor Crmp, the amplifier OTA, thefloating node INN, and the floating node INP of FIG. 3, respectively.

The comparator 151 a may include parasitic capacitors Cp1, Cp2, Cp3 andCp4 in addition to the predetermined pixel capacitor Cpix and thepredetermined ramp capacitor Crmp. The first parasitic capacitor Cp1 maybe formed between an input stage of the first pixel signal VPIX1 and aground terminal. The second parasitic capacitor Cp2 may be formedbetween an input stage of the ramp signal VRMP and the ground terminal.The third parasitic capacitor Cp3 may be formed between the floatingnode INN and the ground terminal. The fourth parasitic capacitor Cp4 maybe formed between the floating node INP and the ground terminal.

Transmission efficiency of the comparator 151 a is determined bycapacitance of capacitors. If capacitances of the pixel capacitor Cpixand the ramp capacitor Crmp as the input capacitor increase,transmission efficiency of comparator 151 a may increase. Ifcapacitances of the parasitic capacitors Cp1, Cp2, Cp3 and Cp4 increase,transmission efficiency of the comparator 151 a may be reduced. Thus, toincrease transmission efficiency of the comparator 151 a, a designchange of reducing capacitances of the parasitic capacitors Cp1, Cp2,Cp3 and Cp4 is needed.

FIG. 5 is a conceptual diagram corresponding to a cross section takenalong the line A-A′ in FIG. 3 to implement a connection relation ofcapacitors illustrated in FIG. 4. Referring to FIGS. 3 through 5, thepixel capacitor Cpix and the ramp capacitor Crmp of the comparator 151 amay be formed by a plurality of layers stacked in the third directionD3. The comparator 151 a may include a capacitor layer and a routinglayer. The capacitor layer may include a first poly layer PC1, a secondpoly layer PC2, and a first metal layer M1. The routing layer mayinclude a third metal layer M3, a fourth metal layer M4, and a fifthmetal layer M5. A second metal layer M2 may be selectively formed tominimize an effect between the capacitor layer and the routing layer. Aninsulating layer may be formed between each layer.

FIG. 5 illustrates a conceptual layout and a thickness of each layer maybe changed depending on a design. A distance between the layers may bechanged depending on a design. A width of each layer may be limitedwithin the first width W1.

The capacitor layer may be formed to provide the predetermined inputcapacitors Crmp and Cpix. The ramp capacitor Crmp may be formed betweenthe first poly layer PC1 and the second poly layer PC2. The rampcapacitor Crmp may also be formed between the second poly layer PC2 andthe first metal layer M1. The first poly layer PC1 and the first metallayer M1 may be connected to each other through an eighth via (VIA8).The ramp signal VRMP may be input to the first poly layer PC1 and thefirst metal layer M1. The second poly layer PC2 may be connected to thefloating node INP. The second parasitic capacitor Cp2 may be formedbetween the first poly layer PC1 and the ground terminal.

Although not illustrated in the drawing, the pixel capacitor Cpix may beformed similar to the ramp capacitor Crmp. The pixel capacitor Cpix maybe formed between the first poly layer PC1 and the second poly layerPC2. The pixel capacitor Cpix may also be formed between the second polycapacitor PC2 and the first metal layer M1. The first poly layer PC1 andthe first metal layer M1 may be connected to each other through anothervia. The first pixel signal VPIX1 may be input to the first poly layerPC1 and the first metal layer M1. The second poly layer PC2 may beconnected to the floating node INN. The second parasitic capacitor Cp2may be formed between the first poly layer PC1 and the ground terminal.The pixel capacitor Cpix may be disposed parallel to the ramp capacitorCrmp in the second direction D2. In FIG. 3, a cross section taken alongthe line A-A′ crosses the ramp capacitor Crmp. Thus, FIG. 5 does notillustrate a cross section of the pixel capacitor Cpix.

The floating nodes (INN, INP) may be formed on the routing layer. Thefourth metal layer M4 may include the floating nodes (INN, INP). Thefloating nodes (INN, INP) may be shielded by the third through fifthmetal layers M3, M4 and M5. The floating node INN may be disposedbetween the third metal layer M3, the fifth metal layer M5, a firstshield line SHD1, and a second shield line SHD2. The first shield lineSHD1 may be connected to the fifth metal layer M5 through a first viaVIA1. The first shield line SHD1 may be connected to the third metallayer M3 through a second via VIA2. The second shield line SHD2 may beconnected to the fifth metal layer M5 through a third via VIA3. Thesecond shield line SHD2 may be connected to the third metal layer M3through a fourth via VIA4. The third metal layer M3, the fifth metallayer M5, the first shield line SHD1, and second shield line SHD2 may beconnected to the ground terminal. Because of this, the third parasiticcapacitor Cp3 may be formed between the floating node INN and the groundterminal.

The floating node INP may be disposed between the third metal layer M3,the fifth metal layer M5, the second shield line SHD2 and a third shieldline SHD3. The second shield line SHD2 may be connected to the fifthmetal layer M5 through the third via VIA3. The second shield line SHD2may be connected to the third metal layer M3 through the fourth viaVIA4. The third shield line SHD3 may be connected to the fifth metallayer M5 through a fifth via VIA5. The third shield line SHD3 may beconnected to the third metal layer M3 through a sixth via VIA6. Thethird metal layer M3, the fifth metal layer M5, the second shield lineSHD2, and third shield line SHD3 may be connected to the groundterminal. Because of this, the fourth parasitic capacitor Cp4 may beformed between the floating node INP and the ground terminal.

Because the third metal layer M3 is connected to the ground terminal,the second parasitic capacitor Cp2 may be formed between the secondmetal layer M2 and the third metal layer M3.

In FIG. 5, because the floating nodes (INN, INP) are shielded by themetal layers (M3, M5) and shield lines (SHD1, SHD2, SHD3) that areconnected to the ground terminal, the parasitic capacitors Cp3 and Cp4may be formed between the floating node INN and the ground terminal andbetween the floating node INP and the ground terminal, respectively.Thus, to increase transmission efficiency of the comparator 151 a, adesign change of reducing capacitances of the parasitic capacitors Cp3and Cp4 is needed.

FIG. 6 is a circuit diagram illustrating a connection relation ofcapacitors according to an example embodiment in one of comparatorsillustrated in FIG. 2. Referring to FIG. 6, a comparator 151 b mayinclude pixel capacitors Cpix1 and Cpix2, ramp capacitors Crmp1 andCrmp2, and an amplifier OTA. The first pixel capacitor Cpix1 and thefirst ramp capacitor Crmp1 are predetermined input capacitors to improvea noise characteristic. The second pixel capacitor Cpix2 and the secondramp capacitor Crmp2 are input capacitors formed by changing a layout ofparasitic capacitors.

The first pixel signal VPIX1 may be transmitted to the amplifier OTAthrough the pixel capacitors Cpix1 and Cpix2. The first pixel capacitorCpix1, the first ramp capacitor Crmp1, the amplifier OTA, the floatingnode INN, and the floating node INP of FIG. 6 correspond to the pixelcapacitor Cpix, the ramp capacitor Crmp, the amplifier OTA, the floatingnode INN, and the floating node INP of FIG. 3, respectively.

The comparator 151 b may include parasitic capacitors Cp1 and Cp2 inaddition to the predetermined pixel capacitors Cpix1 and Cpix2 and thepredetermined ramp capacitors Crmp1 and Crmp2. The first parasiticcapacitor Cp1 may be formed between an input stage of the first pixelsignal VPIX1 and a ground terminal. The second parasitic capacitor Cp2may be formed between an input stage of the ramp signal VRMP and theground terminal.

Transmission efficiency of the comparator 151 b is determined dependingon capacitances of capacitors. If capacitances of the pixel capacitorsCpix1 and Cpix2 and the ramp capacitors Crmp1 and Crmp2 increase,transmission efficiency of the comparator 151 b may increase. Ifcapacitances of the parasitic capacitors Cp1 and Cp2 increase,transmission efficiency of the comparator 151 b may be reduced.

The first pixel capacitor Cpix1 and the first ramp capacitor Crmp1 arecapacitors having a predetermined capacitance. The first pixel capacitorCpix1 and the first ramp capacitor Crmp1 may correspond to the pixelcapacitor Cpix and the ramp capacitor Crmp of FIG. 3, respectively.

The second pixel capacitor Cpix2 and the second ramp capacitor Crmp2 areinput capacitors formed by changing a layout of parasitic capacitors.The second pixel capacitor Cpix2 may be formed by changing a layout ofthe third parasitic capacitor Cp3 of FIG. 4. The second ramp capacitorCrmp2 may be formed by changing a layout of the fourth parasiticcapacitor Cp4 of FIG. 4. Thus, capacitance between the input stage ofthe first pixel signal VPIX1 and the floating node INN may increase.Capacitance between the input stage of the ramp signal VRMP and thefloating node INP may increase. Consequently, transmission efficiency ofthe comparator 151 b may increase.

FIG. 7 is a conceptual diagram corresponding to a cross section takenalong the line A-A′ in FIG. 3 to implement a connection relation ofcapacitors illustrated in FIG. 6. Referring to FIGS. 3, 6 and 7, thefirst pixel capacitor Cpix1 and the first ramp capacitor Crmp1 of thecomparator 151 b may be formed on a capacitor layer stacked in the thirddirection D3. The second pixel Cpix2 and the second ramp capacitor Crmp2of the comparator 151 b may be formed by changing a layout of parasiticcapacitors on a routing layer.

FIG. 7 illustrates a conceptual layout and a thickness of each layer maybe changed depending on a design. A distance between layers may bechanged depending on a design. A width of each layer may be limitedwithin a second width W2. The second width W2 may be set the same as ordifferent from the first width W1 of FIG. 5.

The capacitor layer may be formed to provide the predeterminedcapacitors (Crmp1, Cpix1). The first ramp capacitor Crmp may be formedbetween a first poly layer PC1 and a second poly layer PC2 and betweenthe second poly layer PC2 and a first metal layer M1. The first polylayer PC1 and the first metal layer M1 may be connected to each otherthrough an eleventh via VIA11. The ramp signal VRMP may be applied tothe first poly layer PC1 and the first metal layer M1. The second polylayer PC2 may be connected to the floating node INP. The secondparasitic capacitor Cp2 may be formed between the first poly layer PC1and the ground terminal.

Although not illustrated in FIG. 7, the first pixel capacitor Cpix1 maybe formed similar to the first ramp capacitor Crmp1. The first pixelcapacitor Cpix1 may be formed between the first poly layer PC1 and thesecond poly layer PC2 and between the second poly layer PC2 and thefirst metal layer M1. The first poly layer PC1 and the first metal layerM1 may be connected to each other through another via. The first pixelsignal VPIX may be applied to the first poly layer PC1 and the firstmetal layer M1. The second poly layer PC2 may be connected to thefloating node INN. The first parasitic capacitor Cp1 may be formedbetween the first poly layer PC1 and the ground terminal. The firstpixel capacitor Cpix1 may be disposed parallel to the first rampcapacitor Crmp1 along the second direction D2.

The floating nodes (INN, INP) may be formed on the routing layer. Afourth metal layer M4 may include the floating nodes (INN, INP). A thirdmetal layer M3 may include a third shield line SHD3 and a seventh shieldline SHD7. The fourth metal layer M4 may include a second shield lineSHD2, a fourth shield line SHD4, a sixth shield line SHD6, and an eighthshield line SHD8. A fifth metal layer M5 may include a first shield lineSHD1 and a fifth shield line SHD5.

The floating nodes (INN, INP) may be shielded by the third through fifthmetal layers (M3, M4, M5). The floating node INN may be disposed betweenthe first through fourth shield lines (SHD1 to SHD4). The first shieldline SHD1 may be connected to the second shield line SHD2 through afirst via VIA1. The second shield line SHD2 may be connected to thethird shield line SHD3 through a second via VIA2. The third shield lineSHD3 may be connected to the fourth shield line SHD4 through a third viaVIA3. The fourth shield line SHD4 may be connected to the first shieldline SHD1 through a fourth via VIA4. The first pixel signal VPIX1 may beapplied to the first through fourth shield lines (SHD1 to SHD4). Becauseof this, the second pixel capacitor Cpix2 may be formed between thefloating node INN and an input stage of the first pixel signal VPIX1.

The floating node INP is disposed between fifth through eighth shieldlines (SHD5 to SHD8). The fifth shield line SHD5 may be connected to thesixth shield line SHD6 through a fifth via VIA5. The sixth shield lineSHD6 may be connected to the seventh shield line SHD7 through a sixthvia VIA6. The seventh shield line SHD7 may be connected to the eighthshield line SHD8 through a seventh via VIA7. The eighth shield line SHD8may be connected to the fifth shield line SHD5 through an eighth viaVIA8. The ramp signal VRMP may be applied to the fifth through eighthshield lines (SHD5 to SHD8). Because of this, the second ramp capacitorCrmp2 may be formed between the floating node INP and an input stage ofthe ramp signal VRMP.

Because of the layout change, a parasitic capacitor Cpx may be formedbetween the input stage of the first pixel signal VPIX1 and the inputstage of the ramp signal VRMP. The parasitic capacitor Cpx may be formedbetween the fourth shield line SHD4 and the sixth shield line SHD6. Theparasitic capacitor Cpx may be formed between the third shield line SHD3and the second metal layer M2. However, a reduction of a gain due to theparasitic capacitor Cpx is insignificant.

The second metal layer M2 may be connected to the first metal layer M1through a tenth via VIA10. The second metal layer M2 may be connected tothe seventh shield line SHD7 through a ninth via VIA9.

The comparator 151 b may change parasitic capacitors formed on thefloating nodes (INN, INP) into the second pixel capacitor Cpix2 and thesecond ramp capacitor Crmp2 by changing a layout. The second pixelcapacitor Cpix2 may be connected in parallel to the first pixelcapacitor Cpix1. The second ramp capacitor Crmp2 may be connected inparallel to the first ramp capacitor Crmp1. Thus, capacitance of aninput capacitor in the comparator 151 b may increase. If the capacitanceof the input capacitor increases, transmission efficiency of thecomparator 151 b may increase.

FIG. 8 is a view illustrating a camera system including an image sensoraccording to an example embodiment. A camera system 1000 may include adigital camera. Referring to FIG. 8, the camera system 1000 may includea lens 1100, an image sensor 1200, a motor unit 1300, and an engine unit1400. The image sensor 1200 may include a current stabilizing circuit toprevent an occurrence of a dynamic current according to an exampleembodiment.

The lens 1100 concentrates an incident light into a light receiving areaof the image sensor 1200. The image sensor 1200 may generate RGB data ofa Bayer pattern based on the light introduced through the lens 1100. Theimage sensor 1200 may provide RGB data based on a clock signal CLK. Theimage sensor 1200 may interface with the engine unit 1400 through amobile industry processor interface (MIPI) or a camera serial interface(CSI).

The image sensor 1200 may correspond to the image sensor 100 of FIG. 1.The image sensor 1200 may include a comparison circuit that may change aparasitic capacitor into an input capacitor by changing a layout. Thus,the image sensor 1200 may include a comparison circuit having improvedtransmission efficiency.

The motor unit 1300 may adjust a focus of the lens 1100 or perform ashuttering in response to a control signal CTRL received from the engineunit 1400. The engine unit 1400 controls the image sensor 1200 and themotor unit 1300. The engine unit 1400 may generate YUV data including aluminance component, a difference between the luminance component and ablue component, and a difference between the luminance component and ared component, or generate compressed data (e.g., a joint photographyexpert group (JPEG)) based on RGB data received from the image sensor1200.

The engine unit 1400 may be connected to a host/application 1500. Theengine unit 1400 may provide YUV data or JPEG data to thehost/application 1500 based on a master clock MCLK. The engine unit 1400may interface with the host/application 1500 through a serial peripheralinterface (SPI) or an inter integrated circuit (I²C).

FIG. 9 is a block diagram illustrating a configuration of an electronicdevice including an image sensor according to an example embodiment andinterfaces of the electronic device. An electronic device 2000 may beembodied by a data processing device that can use or support aninterface protocol suggested by a MIPI union. The electronic device 2000may be one of a mobile communication terminal, a personal digitalassistant (PDA), a portable media player (PMP), a smart phone, a tabletcomputer, a wearable device, etc.

The electronic device 2000 may include an application processor 2100,displays 2220 and 2221, and image sensors 2230 and 2231. The applicationprocessor 2100 may include a DigRF master 2110, a display serialinterface (DSI), a DSI host 2120, a camera serial interface (CSI), and aphysical layer 2140.

The DSI host 2120 may communicate with a DSI device 2225 according toDSI. The DSI host 2120 may include an optical serializer SER. The DSIdevice 2225 may include an optical deserializer DES. The display 2220may communicate with a DSI device 2226 of the display 2221 according toDSI. The DSI device 2225 may further include an optical serializer SERand the DSI device 2226 may include an optical deserializer DES. Thedisplay 2221 may not be directly connected to the application processor2100.

The application processor 2100 may directly control the DSI device 2226of the display 2221. The display 2220 may convert a request formatreceived from the application processor 2100 and provide the convertedrequest to the display 2221. The display 2220 may transmit a requestincluding a port identifier to the display 2221. The display 2221 mayset or change a communication environment based on the transmittedrequest.

The CSI host 2130 may communicate with a CSI device 2235 of the imagesensor 2230 according to CSI. The CSI host 2130 may include an opticaldeserializer DES. The CSI device 2235 may include an optical serializerSER. The image sensor 2230 may communicate with a CSI device 2236 of theimage sensor 2231 according to CSI. The CSI device 2235 may furtherinclude an optical deserializer DES and the CSI device 2236 may includean optical serializer SER. The image sensor 2231 may not be directlyconnected to the application processor 2100.

The application processor 2100 may directly control the CSI device 2236of the image sensor 2231. The image sensor 2230 may convert a requestformat received from the application processor 2100 and provide theconverted request to the image sensor 2231. The image sensor 2230 maytransmit a request including a port identifier to the image sensor 2231.The image sensor 2231 may set or change a communication environmentbased on the transmitted request.

The image sensor 2231 may correspond to the image sensor 100 of FIG. 1.The image sensor 2231 may include a comparison circuit that may change aparasitic capacitor into an input capacitor by changing a layout. Thus,the image sensor 2231 may include a comparison circuit having improvedtransmission efficiency.

The electronic device 2000 may further include a radio frequency (RF)chip 2240 that communicates with the application processor 2100. The RFchip 2240 may include a physical layer 2242, a DigRF slave 2244, and anantenna 2246. The physical layer 2242 of the RF chip 2240 may exchangedata with the physical layer 2140 of the application processor 2100using a DigRF interface suggested by a MIPI union.

The electronic device 2000 may further include a working memory 2250, anembedded storage device 2251, and a card storage device 2252. Theworking memory 2250, the embedded storage device 2251, and the cardstorage device 2252 may store data provided from the applicationprocessor 2100. Further, the working memory 2250, the embedded storagedevice 2251, and the card storage device 2252 may provide the storeddata to the application processor 2100.

The working memory 2250 may temporarily store data processed or to beprocessed by the application processor 2100. The working memory 2250 mayinclude a volatile memory such as a static random access memory (SRAM),a dynamic RAM (DRAM), a synchronous DRAM (SDRAM), etc. and/or anonvolatile memory such as a flash memory, a phase-change RAM (PRAM), amagnetic RAM (MRAM), a resistive RAM (ReRAM), a ferroelectric RAM(FRAM), etc.

The electronic device 2000 may communicate with an externaldevice/system through a communication module such as a wordinteroperability for microwave access (WiMAX) 2260, a wireless localarea network (WLAN) 2262, an ultra-wideband (UWB) 2264, etc. Inaddition, the electronic device 2000 may communicate with an externaldevice/system according to at least one of various wirelesscommunication protocols such as a long term evolution (LTE), a globalsystem for mobile communication (GSM), a code division multiple access(CDMA), a Bluetooth, a near field communication (NFC), a WiFi, a radiofrequency Identification (RFID), and/or at least one of various wiredcommunication protocols such as a transfer control protocol/internetprotocol (TCP/IP), a universal serial bus (USB), a small computer systeminterface (SCSI), a mobile PCIe (M-PCIe), a Firewire, etc.

The electronic device 2000 may further include a speaker 2270 and amicrophone 2275 for processing voice information. Further, theelectronic device 2000 may further include a global positioning system(GPS) 2280 for processing location information. The electronic device2000 may further include a bridge chip 2290 for managing a connectionwith peripheral devices.

The electronic device 2000 may communicate with a user adopting varioususer interfaces. The user interface may include user input interfacessuch as a keyboard, a keypad, a button, a touch panel, a touch screen, atouch pad, a touch ball, a camera, a microphone, a gyroscope sensor, avibration sensor, a piezoelectric element, etc. The user interface mayinclude user output interfaces such as a liquid crystal display (LCD),an organic light emitting diode (OLED) display, an active matrix OLED(AMOLED) display, a LED, a speaker, a motor, etc.

A comparison circuit according to an example embodiment and an imagesensor including the comparison circuit may include a capacitorstructure that may improve transmission efficiency. According to exampleembodiments, the comparison circuit may improve transmission efficiencythrough a layout that makes use of a parasitic capacitor formed at afloating node as an input capacitor.

As is traditional in the field of the inventive concepts, exampleembodiments are described, and illustrated in the drawings, in terms offunctional blocks, units and/or modules. Those skilled in the art willappreciate that these blocks, units and/or modules are physicallyimplemented by electronic (or optical) circuits such as logic circuits,discrete components, microprocessors, hard-wired circuits, memoryelements, wiring connections, and the like, which may be formed usingsemiconductor-based fabrication techniques or other manufacturingtechnologies. In the case of the blocks, units and/or modules beingimplemented by microprocessors or similar, they may be programmed usingsoftware (e.g., microcode) to perform various functions discussed hereinand may optionally be driven by firmware and/or software. Alternatively,each block, unit and/or module may be implemented by dedicated hardware,or as a combination of dedicated hardware to perform some functions anda processor (e.g., one or more programmed microprocessors and associatedcircuitry) to perform other functions. Also, each block, unit and/ormodule of the example embodiments may be physically separated into twoor more interacting and discrete blocks, units and/or modules withoutdeparting from the scope of the inventive concepts. Further, the blocks,units and/or modules of the example embodiments may be physicallycombined into more complex blocks, units and/or modules withoutdeparting from the scope of the inventive concepts.

While the inventive concept has been described with reference to exampleembodiments, it will be apparent to those skilled in the art thatvarious changes and modifications may be made without departing from thespirit and scope of the inventive concept. Therefore, it should beunderstood that the above example embodiments are not limiting, butillustrative.

What is claimed is:
 1. A comparison circuit comprising: an amplifierconfigured to receive a pixel signal and a ramp signal to perform acorrelated double sampling operation; a first pixel capacitor connectedto the amplifier through a first floating node and configured totransmit the pixel signal; a first ramp capacitor connected to theamplifier through a second floating node and configured to transmit theramp signal; a second pixel capacitor connected in parallel to the firstpixel capacitor; and a second ramp capacitor connected in parallel tothe first ramp capacitor, wherein the second pixel capacitor is formedbetween the first floating node and first peripheral routing lines, andthe second ramp capacitor is formed between the second floating node andsecond peripheral routing lines, wherein a routing layer is stacked on acapacitor layer in a direction perpendicular to a substrate, wherein thefirst pixel capacitor and the first ramp capacitor are formed in thecapacitor layer, and wherein the second pixel capacitor, the second rampcapacitor, and the first and second peripheral routing lines are formedin the routing layer.
 2. The comparison circuit of claim 1, wherein thefirst floating node is shielded by the first peripheral routing lines,and wherein the pixel signal is input to the first peripheral routinglines.
 3. The comparison circuit of claim 1, wherein the second floatingnode is shielded by the second peripheral routing lines, and wherein theramp signal is input to the second peripheral routing lines.
 4. Thecomparison circuit of claim 1, wherein the first pixel capacitor and thefirst ramp capacitor are input capacitors having a predeterminedcapacitance.
 5. The comparison circuit of claim 1, wherein the secondpixel capacitor is a parasitic capacitor formed between the firstfloating node and the first peripheral routing lines, and wherein thesecond ramp capacitor is a parasitic capacitor formed between the secondfloating node and the second peripheral routing lines.
 6. The comparisoncircuit of claim 1, wherein in the capacitor layer, the first pixelcapacitor is disposed parallel to the first ramp capacitor in adirection along the substrate.
 7. The comparison circuit of claim 1,wherein in the capacitor layer, the first pixel capacitor and the firstramp capacitor are formed by stacking a plurality of conductive layerson the substrate along the direction perpendicular to the substrate, andwherein a plurality of insulating layers are stacked between theplurality of conductive layers.
 8. The comparison circuit of claim 1,wherein a length of the first floating node is the same as a length ofthe second floating node.
 9. An image sensor comprising: a sensor arrayconfigured to convert a light into an electrical signal to generate apixel signal; a ramp signal generator configured to generate a rampsignal; and a comparison circuit configured to receive the pixel signaland the ramp signal to perform a correlated double sampling operation,wherein the comparison circuit comprises: an amplifier configured toperform the correlated double sampling operation; a first pixelcapacitor connected to the amplifier through a first floating node andconfigured to transmit the pixel signal; a first ramp capacitorconnected to the amplifier through a second floating node and configuredto transmit the ramp signal; a second pixel capacitor connected inparallel to the first pixel capacitor; and a second ramp capacitorconnected in parallel to the first ramp capacitor, wherein the secondpixel capacitor is formed between the first floating node and firstperipheral routing lines, and the second ramp capacitor is formedbetween the second floating node and second peripheral routing lines,wherein a routing layer is stacked on a capacitor layer in a directionperpendicular to a substrate, wherein the first pixel capacitor and thefirst ramp capacitor are formed in the capacitor layer, and wherein thesecond pixel capacitor, the second ramp capacitor, and the first andsecond peripheral routing lines are formed in the routing layer.
 10. Theimage sensor of claim 9, wherein the first floating node is shielded bythe first peripheral routing lines, and wherein the pixel signal isinput to the first peripheral routing lines.
 11. The image sensor ofclaim 9, wherein the second floating node is shielded by the secondperipheral routing lines, and wherein the ramp signal is input to thesecond peripheral routing lines.
 12. The image sensor of claim 9,wherein the first pixel capacitor and the first ramp capacitor are inputcapacitors having a predetermined capacitance.
 13. The image sensor ofclaim 9, wherein the second pixel capacitor is a parasitic capacitorformed between the first floating node and the first peripheral routinglines, and wherein the second ramp capacitor is a parasitic capacitorformed between the second floating node and the second peripheralrouting lines.
 14. A comparison circuit comprising: an amplifierconfigured to receive a pixel signal and a ramp signal to perform acorrelated double sampling operation; an input capacitor comprising apixel capacitor and a ramp capacitor and having a predeterminedcapacitance; and a plurality of parasitic capacitors, wherein aparasitic capacitor, among the parasitic capacitors, formed at afloating node between the input capacitor and the amplifier is convertedinto an input capacitor by changing a layout of the comparison circuitto increase capacitance of the input capacitor, the changing the layoutof the comparison circuit comprising connecting the parasitic capacitorformed at the floating node in parallel to the input capacitor, whereina routing layer is stacked on a capacitor layer in a directionperpendicular to a substrate, wherein the pixel capacitor and the rampcapacitor are formed in the capacitor layer, and wherein the parasiticcapacitor is formed in the routing layer.
 15. The comparison circuit ofclaim 14, wherein the parasitic capacitor is formed between the floatingnode and peripheral routing lines.
 16. The comparison circuit of claim14, wherein in the capacitor layer, the pixel capacitor is disposedparallel to the ramp capacitor in a direction along the substrate. 17.The comparison circuit of claim 14, wherein in the capacitor layer, thepixel capacitor and the ramp capacitor are formed by stacking aplurality of conductive layers on the substrate along the directionperpendicular to the substrate, and wherein a plurality of insulatinglayers are stacked between the plurality of conductive layers.